(a) Field of the Invention
The present invention relates to a method of manufacturing a diazo copying material suitable for use in preparing a secondary original.
(B) Description of the Prior Art
The so-called secondary original is an original obtained by copying a primary original for the purpose of providing a substitute for said primary original. The secondary original is generally formed on a diazo copying material consisting of a transparent of translucent paper support or plastic film provided with a precoating layer and a photosensitive layer formed thereon.
Accordingly, an image formed on said secondary original is desirably one with the least possible ultraviolet-ray transmission, to wit, a superior light-shielding property, and at the same time, it is desirably one with a color tone easy to see as far as possible, to wit, the highest possible visual density, for the sake of facilitating later entry in the secondary original as occasion demands. Besides, inasmuch as the diazo copying process is the most inexpensive one among varieties of copying processes, in order to make the most of this characteristic, it is to be desired to provide an inexpensive diazo copying material for use in preparing a secondary original.
However, a paper support for a secondary original, which support is processed for transparency or transluceny, tends to be deprived of the surface porousness inherent in paper and a plastic film is high in the smoothness of the surface thereof so that uniform coating of a water-dispersible liquid comprising a porous powder and a binding agent as principal ingredients thereof on such supports, which is generally adopted as a means of forming a high density image on a diazo photosensitive paper, has hitherto been difficult to practice, and unevenness of the coating would take place. Consequently, it is infeasible to obtain a uniform, clear-cut image even when a photosensitive layer is further provided on the precoating layer.
In the prior art, therefore, an organic solvent-type dispersion comprising a porous powder and a binding agent has been applied as a precoating liquid onto a paper support. This conventional method, however, is defective in that safety during the stage of manufacture is not ensured, the resulting secondary original is costly, and, even though there can admittedly be obtained an image with high density to some extent in the case of a dry developing process employing ammonia gas as the developer because of infiltration of said ammonia gas in the binding agent, in the case of the wet developing process employing an aqueous solution of an alkali or a coupler as a developer and the semi-dry developing process employing an organic solvent containing an alkali or a coupler as liquid developer, infiltration and diffusion of the developer becomes insufficient and there can be obtained no more than an image having low density.